German Patent Application No. 195 31 771.8 describes a method and a device for determining an angular velocity of a polyphase machine operated by field orientation without a transmitter.
The present invention is based on the finding that under steady-state operating conditions, there is a difference EQU .DELTA..omega./.omega..sub.* =.omega./.omega..sub.* -.omega./.omega..sub.* =.DELTA.n=n-n (1)
between a normalized rotational speed n of the model of the machine and a normalized speed n of the polyphase machine.
According to German Patent Application No. 195 31 771.8, in steady-state operation, the following formal relationship exists between normalized rotational speed difference .DELTA.n and system deviation .DELTA..perp. at the input of the equalizing controller according to the older German patent application: ##EQU1##
where
##EQU2## is the model rotor frequency ##EQU3## is the model stator frequency ##EQU4## is the leakage factor of the polyphase machine ##EQU5## is the time constant ratio ##EQU6## is the selected reference space vector
The ".about." symbols above notations in the equation indicate that only steady-state operating states are taken into account.
According to equation 2, the magnitude of steady-state transfer factor {tilde over (u)} in general changes considerably as a function of stator frequency n.sub.s and rotor frequency n.sub.r as operating parameters, which characterize a steady-state operating point of the polyphase machine. FIG. 3 illustrates this relationship for the case when normalized rotor flux space vector .psi..sub.r is selected as reference space vector ##EQU7##
for splitting the stator current model space vector and the stator current real space vector. Stator frequency n.sub.s and rotor frequency n.sub.r as operating parameters are linked together via normalized rotational speed n according to the following equation: EQU n.sub.s =n+n.sub.r
Normalization to rotor break-down circular frequency .omega..sub.rK =R.sub.r /L.sub.94 and the symbol "-" for characterization of steady-state operation are described in the article "Schnelle Drehmomentregelung im gesamten Drehzahlbereich eines hochausgenutzten Drehfeldantriebs" (Fast torque control in the entire rpm range of a highly utilized rotational field drives), printed in the German journal Archiv fur Elektrotechnik (Archive for Electrical Engineering), 1994, volume 77, pages 289 through 301.